Are the Earth's magnetic poles moving? How do navigators adjust to this change?

December 29, 1997

The answer comes from Paul Perreault, marketing manager for university and government research programs at Trimble Navigation
Ltd., a manufacturer of advanced navigation systems.

Image: Canadian National Geomagnetism Program

WANDERING POLE. The
North magnetic pole has moved steadily northward at an average rate of 10 kilometers per year since it was first located in 1831.

The earth's geographic poles are generally right where you would expect them to be: at the two opposing points about
which the Earth seems to rotate. Magnetic poles used in compass navigation are another matter altogether. And neither pole pair is completely
stationary.

The North magnetic pole is at a point where a dipping compass--a compass that allows the needle to move freely in a vertical
plane (as opposed to the horizontal needle movements seen in most compasses)--points straight down into the earth. The South magnetic pole is
the point where a dipping compass points up. A dipping compass points horizontally on the Earth's magnetic equator, also called the Earth's dip
equator.

The magnetic poles are quite distant from their geographic counterparts. The North magnetic pole is located to the south in Northern
Canada; the geographic South pole is at the center of the Antarctic continent, but the magnetic pole is hundreds of miles away, near the coast. In
regions near the magnetic poles, compasses are virtually useless.

Complicating this issue is that these pole positions are not static--for either
magnetic or geographic poles. The location of the North geographic pole wanders in a small erratic circle-like path, called the "Chandler wobble."
This motion is less than 6 meters per year on the surface; a worldwide network of very precise global positioning satellite (GPS) receivers is used to
determine this wander.

The magnetic poles are far more restless. They move under the influence of the dynamo currents in the Earth's core, as
well as electric currents flowing in the ionosphere, the radiation belts and the Earth's magnetosphere. The North magnetic pole seems to be
moving northward at an average rate of 10 kilometers per year. Yet there is also some elliptical motion to this general trend. On any given day, the
magnetic pole may be as much as 80 kilometers away from its average position, depending on the geomagnetic disturbances in the ionosphere and
magnetosphere.

Modern navigators normally are not affected by the wandering of the poles because they can regularly determine their
position from satellites and Earth-based observatories. The degree of difference between the position of these two poles when seen at various
locations is called magnetic declination. These angles allow navigators to determine their actual geographic position. Charts and handbooks for
navigation regularly update these values and are published by government agencies.

Maritime and air navigation regulations require use of
these up-to-date charts and tables. Without GPS, the navigator would use a new version of the chart or table. With GPS, navigators update their
receiver database by purchasing new data from the Government or from the GPS manufacturer and loading it into the onboard GPS unit.